Modern aircraft are increasingly incorporating resin composite materials in the construction of a variety of components because the weight/strength ratio of many composite materials exceeds that of many metals. In a typical construction of composites used for modern aircraft, each layer of the composite is formed with plies of resinous matrix material reinforced with fiber. An example is graphite or carbon reinforced epoxy.
While providing many advantages in terms of strength and weight, composite materials pose unique problems when one is attempting to repair damaged areas. One problem which frequently occurs is repairing damaged composite components while retaining the structural integrity of the original component. Since loads in composite materials are carried by the fibers of the material, a repair preparation must expose each respective layer of fiber of a composite workpiece for bonding replacement materials to the workpiece in a manner that permits load transfer between each layer of the part and each layer of the patch. Failure to properly bond the fibers of each layer of the composite workpiece may result in the workpiece not being able to support design loads and damage to the composite.
The repair of composite materials therefore requires that the damaged area of a composite workpiece be removed in a manner to expose the fibers of each layer for bonding to the fibers of the patch. Typically, damaged composite material is removed from a workpiece in preparation for repair by a process known as "scarfing." Scarfing provides a repair region, surrounding a damaged area, having beveled or angled walls to receive new composite material and provides a contact surface for each layer or ply. Preferably, the repair region has a complex shape, such as a spherical or ovular shape, so that the repair plies of the patch may be placed in the repair region in layers wherein the fibers of each layer of the patch are bonded to the fibers of a respective layer of the composite workpiece. In this manner, the load bearing capability of the repaired composite workpiece is maximized.
Scarfing a workpiece requires an apparatus for providing tightly controlled dimensions over complex repair regions. Particularly, the angle of the walls of the repair region, i.e., the taper angle, must be carefully controlled to expose the fibers of each layer of the workpiece. Scarfing a workpiece having a complex surface requires apparatus capable of providing the tightly controlled dimensions, i.e., the taper angle, on the complex surface. This requires the scarfing apparatus to alter the positioning of the cutting instrument in response to alterations in the radius, or contour, of the surface.
Several tools have been developed that are ideal for scarfing flat surfaces of a workpiece. An example of such a tool is that disclosed in U.S. patent application Ser. No. 284,137 entitled "Mechanical Scarfing Apparatus," filed Dec. 13, 1988, the disclosure of which is incorporated herein, in its entirety by the foregoing reference. The scarfing apparatus disclosed in U.S. Ser. No. 234,137 is capable of scarfing complex cuts in a planar workpiece to maximize the load bearing capability of the repaired workpiece, as discussed above. However, the scarfing apparatus is difficult to use on a workpiece having a complex surface.
Soviet Union Inventor's Certificate No. 537,762, issued 1977 discloses a router mounted on the end of a shaft and an adjustment arm for adjusting the angle of the router. While this device can create complex repair regions into a flat surface of a workpiece, there does not appear to be any disclosure of apparatus for creating a complex repair region in a workpiece having a complex surface. The Inventor's Certificate also does not appear to disclose a mechanism for moving the router in a lateral direction. Accordingly, the apparatus disclosed in the Inventor's Certificate is not appropriate for scarfing a workpiece having a complex structure.
Another example of an apparatus for supporting a cutting instrument is shown in U.S. Pat. No. 2,638,136. This device includes a support structure that couples a router to a plurality of cross supports over a workpiece. In this invention, the cross-support members restrict movement of the router to a single plane which is perpendicular to the cross-support members. The router is adapted to pivot about the support structure, thereby enabling complex regions to be scarfed in a flat surface. However, no apparatus is shown that enables the position of the router to be controlled, at least in part, to follow the contour of the workpiece. Accordingly, the apparatus disclosed in U.S. Pat. No. 2,638,136 is not appropriate for preparing a close tolerance scarfing in a workpiece having a complex surface.
It is desirable, therefore, to provide scarfing apparatus which is responsive to the contour of the workpiece while adjusting the position of the cutting instrument. It is also desirable to provide scarfing apparatus capable of precision control of a cutting instrument on a variety of complex surfaces. It is further desirable to provide scarfing apparatus for generating tapered cuts tangent to the surface of a complex structure with precise control over the depth, quality, and angle of the cut.